A Dublin accent is just made to say "arse": in Colum McCann's gentle brogue the word becomes a beautiful thing. This, in a sense, is what his fiction does too – few contemporary writers are better at extracting the sublime from the base.

McCann had six novels to his name by the time he turned 40, but it was 2009's best-selling and prize-scooping Let the Great World Spin that made him an international name. The event on which its several narratives hinge is Philippe Petit's 1974 tightrope walk between the twin towers of the World Trade Centre and in this way it manages to be a novel about 9/11 that never mentions 9/11 – an elegy as heightened and finely tuned as that wire Petit danced across decades before the towers fell. All of the book's characters have experienced some form of loss, and one bereaved mother observes that, "everything in New York is built upon another thing, nothing is entirely by itself, each thing as strange as the last, and connected". If you omit "New York", that sentence might also serve to describe McCann's approach to fiction. TransAtlantic, the 48-year-old's first novel since Let the Great World Spin, is a kind of cat's cradle of transatlantic journeys, all connected, all built on another thing.

McCann, who's lived in New York for almost two decades, had suggested a drink at a downtown Irish pub named – what else – Ulysses. "I actually opened this bar with Frank McCourt 10 years ago," he says. "Did you ever meet Frank? Beautiful man. We didn't cut a ribbon, we actually read Ulysses."

McCann is a talker of the best kind. He chats on happily, peppering me with questions, and it's a while before I can steer him on to TransAtlantic. Three of its stories come from real-life historical figures: the abolitionist movement leader and former slave Frederick Douglass, the US senator and Northern Ireland peace envoy George Mitchell, and Alcock and Brown, the two first world war veterans who made the first flight from Britain to America in 1919. It's their journey that forms the book's bravura opening section. Those two, he says, came easily, it was Douglass who gave him grief. He liked him, he disliked him, and it was when he realised "these two contradictory things actually worked together, they were both true," that he finally gained traction with the story.

"I did think," he adds, "about just doing Douglass but then it would have been a historical novel and" – he pulls a face – "I hate the term … It just seems steeped in aspic. I mean every novel's a historical novel anyway. But calling something a historical novel seems to put mittens on it, right? It puts manners on it. And you don't want your novels to be mannered."

The character of Lily, a 19th-century maid who makes her way to America, presented herself to him, as did Lottie, her granddaughter, who ends up meeting Alcock and Brown as they prepare for their flight.

"And I was like: well this is strange and this is odd, but those women are there for a reason. Then it made absolute sense to me because I was dealing with three strands of male non‑fiction, and with three strands of female fiction that folded over on to one another." He adds: "I said in an interview about 12 years ago that writing about real biographical figures showed a sort of failure of the writer's imagination."

This is the first time, though, that he's taken a still-living person for a character – George Mitchell, instrumental in brokering the Good Friday agreement and a man McCann regards, unreservedly, as a hero. McCann wrote to Mitchell's wife, who happened to have read Dancer in her book group and so responded warmly, happy to set him straight on details such as the colour of Mitchell's shoes (black, not brown).

"But did I feel trepidation?" he says. "No. I feel no trepidation whatsoever. I like the idea – [Clifford] Geertz talks about it – that the real is as invented as the imaginary. William Maxwell has this idea that memory is mostly lies anyway and it's how we choose to invent it. I don't believe a poet has a better hold on truth or morality than a fiction writer has. And I don't think a fiction writer has anything over a journalist. It's all about the good word, properly inserted."

McCann began his career as a journalist. Why write novels instead of journalism? "If I were writing journalism I'd know where it is that I'm supposed to go. With this, I have no idea where it's going to go or what's going to happen with it."

McCann's own transatlantic journey came when he was 18, fired up on the fiction of Ginsberg, Kerouac and Ferlinghetti – "young man's literature", he says. These were books that his father, a pro footballer who went on to become literary editor at the Dublin Evening Press, brought back for him from business trips to the US. After a short spell as a runner at Universal Press in New York, McCann returned to Dublin to work at the Irish Press.

"I had my own page. It was really awful. Hideous stuff. It was supposed to be for young people – what album came out, 'designer stubble' – all this sort of shit. It was awful. But I enjoyed it. My friends and I had a good laugh. We got invited to all the great parties and stuff."

After a while though, he realised that his literary ambitions eclipsed notes on designer stubble. At the start of one summer, aged 21, he took himself off to Cape Cod, bought an old typewriter, loaded it up with one long ream of paper a la Kerouac ("I know, ridiculous") and sat down to write his masterpiece. When the summer ended he took stock of his output: a foot and a half of paper.

"And I was like: shit, I don't know anything. I had," he says, "all the desire and none of the story."

So he set out in search of one, or rather many, on a bicycle adventure across America that proved the most formative experience of his life. When I ask him to tell me some of his favourite memories he blows his cheeks out, shakes his head: "There's so many." There was San Francisco ("cycled across the Golden Gate Bridge, went down to City Lights bookshop, cried my eyes out"), a moment of grace in a New Mexico diner ("being close to penniless, counting out pennies on the counter and slipping on my cycling gloves afterwards and finding a $20 bill, slipped in, anonymously – somebody beautiful"), and then a long stint teaching juvenile offenders that he'd met at a church service in Texas. "One reason I haven't written about it is because I'm still writing about it, if you know what I mean? All of those stories are still coming out."

He recounts getting lost in Utah and nearly dying. "I was really reckless. But I think that's part of the beauty of being a writer – you continue to be reckless. You can jump off the edge. Vonnegut said it beautifully – he said we should be continually jumping off the edge of a cliff and developing our wings on the way down. And that's what it feels like."

Even if it might not look like it: "I invented a desk where I actually sit in a cupboard," he says. "I lock myself in and then it becomes a different world. Yeah I'm very boring really: I live on the Upper East Side, a block from the park. I have three kids. I go for a jog around the park every day with my dog."

He also teaches creative writing at Hunter College, where he likes to welcome each year's intake by telling them he can't teach them anything. "I don't really know what an adverb is. A dangling participle? That sounds really rude. I don't know what character is, really. Plot seems vaguely juvenile to me. It's all about language, it's all about how you apply it to the page."

I tell him that my favourite line in the novel begins the Emily section: "Stories began for her as a lump in the throat," and McCann repeats the line out loud, reflective and pleased. "Yeah that was probably my most written paragraph about the act of writing. I think part of it is you have this thing inside you that you have to confront and you don't really know what it is. When finally I felt it came to me, it was a huge release and then that lump in the throat was gone."

McCann has long been preoccupied with the Portugese term "saudade", the longing for something lost. In an earlier interview he admitted that, "nearly all of my characters are away from home and trying to find a way back home" and that's never been more true than with this novel. I ask him if he ever feels the need to check himself from becoming overly sentimental.

"Yes," he says very firmly. "I do. Absolutely. I try to balance my sentiment out and parcel it … I'd be willing to take every cynic on in the department of cynicism – I can get down and dark just as quick as anybody else, I'm not afraid of that – but I also find it kind of useless."

At the same time: "I don't want it to be all cool and poised and polished. Because that's completely uninteresting to me. So you do have to go into territory where you look at yourself and go" – he mimes confronting a page in front of him – "'Wow, that is terrible what I just did!' … But believing that this stuff matters – I've seen it in operation."

He is referring to Narrative 4, a global charity he has co-founded, dedicated to creating social change through storytelling. "So let's say it's kids from Limerick and kids from Chicago. They'll pair up and then they'll tell each other their story. And then they'll come back into a group and tell that story. But the real beautiful kicker is, you have to tell the other person's story. It's about developing empathy."

By this point, the afternoon has long faded to evening and the photographer has joined us, as well as the pub's owner, Danny McDonald, a fellow Irishman and old friend. McCann is talking about fiction versus nonfiction when he interrupts himself: "The one thing that we can't forget is that, in the end, it's also a form of entertainment. And we get so far up our own arses that I forget sometimes, that you've got to entertain your reader as well, you've got to look after them." As the bar noise swells, the empty Guinness glasses crowd and McCann talks on.